Respiratory apparatus with improved flow-flattening detection

ABSTRACT

In a respiratory apparatus for treatment of sleep apnea and other disorders associated with an obstruction of a patient&#39;s airway and which uses an airflow signal, an obstruction index is generated which detects the flattening of the inspiratory portion of the airflow. The obstruction index is used to differentiate normal and obstructed breathing. The obstruction index is based upon different weighting factors applied to sections of the airflow signal thereby improving sensitivity to various types of respiration obstructions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/611,315, filed on Dec. 15, 2006 which is a continuation of U.S.application Ser. No. 11/325,169 filed Jan. 4, 2006(now U.S. Pat. No.7,159,588), which is a continuation of U.S. application Ser. No.10/950,926 filed Sep. 27, 2004 (now U.S. Pat. No. 7,013,893), which is acontinuation of Ser. No. 09/924,325 filed Aug. 8, 2001 (now U.S. Pat.No. 6,814,073) which claims priority filing date from U.S. ProvisionalApplication No. 60/228,630 filed Aug. 29, 2000, all of which are herebyincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to a method and apparatus for detectingobstruction of the airway of a patient. More specifically, the inventioninvolves an improved method and apparatus for detecting obstruction,either partial or complete, based upon a flattened measure of aninspiratory portion of respiratory airflow. The method is useful inpatient ventilators such as those used in the diagnosis and treatment ofrespiratory conditions including sleep apnea or hypopnea.

BACKGROUND OF THE INVENTION

The dangers of obstructed breathing during sleep are well known inrelation to the Obstructive Sleep Apnea (OSA) syndrome. Apnea, hypopneaand heavy snoring are recognized as causes of sleep disruption and riskfactors in certain types of heart disease.

The monitoring of upper airway pressure-flow relationships inobstructive sleep apnea has been described in Smith et al., 1988, J.Appl. Physiol. 64: 789-795. FIG. 1 of that article shows polygraphicsleep recordings at varying levels of increasing nasal pressure. It wasnoted that inspiratory volumetric flow plateaued in certain breathssuggesting the presence of airflow limitation. Pressure-flow curves wereconstructed by plotting midinspiratory airflow against either maskpressure or endoesophageal pressure. The pressure-flow plots of nasalpressure against mean midinspiratory flow were then fit by least-squareslinear regression to calculate resistance upstream to the collapsiblesite.

The effect of positive nasal pressure on upper airway pressure-flowrelationships has been described in Schwartz et al., 1989, J. ApplPhysiol. 66: 1626-1634. FIG. 4 of the article shows that pressure-flowtracings plateau at a low pressure level. It was further shown when thepressure was increased, flow did not plateau.

The common method of treatment of these syndromes is to administerContinuous Positive Airway Pressure (CPAP). The procedure foradministering CPAP treatment has been documented in both the technicaland patent literature. Briefly stated, CPAP treatment acts as apneumatic splint of the airway by the provision of a positive pressure,usually in the range 4-20 cm H₂O. The air is supplied by a motor drivenblower whose output passes via an air delivery device to sealinglyengage a patient's airway. A mask, tracheotomy tube, endotracheal tube,nasal pillows or other appropriate device may be used. An exhaust portis provided in a delivery tube proximate to the air delivery device.Other forms of CPAP, such as bi-level CPAP, and self-titrating CPAP, aredescribed in U.S. Pat. Nos. 5,148,802 and 5,245,995 respectively.

With regard to the control of CPAP treatment, various techniques areknown for sensing and detecting abnormal breathing patterns indicativeof obstruction. For example, U.S. Pat. No. 5,245,995 describes howsnoring and abnormal breathing patterns can be detected by inspirationand expiration pressure measurements while sleeping, thereby leading toearly indication of preobstructive episodes or other forms of breathingdisorder. Particularly, patterns of respiratory parameters aremonitored, and CPAP pressure is raised on the detection of pre-definedpatterns to provide increased airway pressure to ideally prevent theoccurrence of the obstructive episodes and the other forms of breathingdisorder.

Similarly, U.S. Pat. No. 5,335,654 (Rapoport) lists several indices saidto be indications of flow limitation and/or partial obstruction patternsincluding: (1) The derivative of the flow signal equals zero; (2) Thesecond derivative between peaks of the flow signal is zero for aprolonged interval; (3) The ratio of early inspirational flow tomidinspirational flow is less than or equal to 1. The patent furtherlists events said to be indications of obstructions: (1) Reduced slopeof the line connecting the peak inspiratory flow to the peak expiratoryflow; (2) Steep upward or downward stroke (dV/dt) of the flow signal;and (3) Ratio of inspiratory flow to expiratory flow over 0.5.

U.S. Pat. No. 5,645,053 (Remmers) describes calculating a flatnessindex, wherein flatness is defined to be the relative deviation of theobserved airflow from the mean airflow. In Remmers, individual values ofairflow are obtained between 40% and 80% of the inspiratory period. Themean value is calculated and subtracted from individual values ofinspiratory flow. The individual differences are squared and divided bythe total number of observations minus one. The square root of thisresult is used to determine a relative variation. The relative variationis divided by the mean inspiratory airflow to give a relative deviationor a coefficient of variation for that breath.

In commonly owned U.S. Pat. No. 5,704,345, Berthon-Jones also disclosesa method for detecting partial obstruction of a patient's airway.Generally, the method involves a determination of two alternativeobstruction index values based upon the patient's monitored respiratoryairflow. Either obstruction index may then be compared to a thresholdvalue. Essentially, the index values may be characterized as shapefactors that detect a flattening of an inspiratory portion of apatient's respiratory airflow. The first shape factor involves a ratioof the mean of a midportion of the inspiratory airflow of the breathingcycle and the mean of the inspiratory airflow. The formula for shapefactor 1 is as follows:

${{shapefactor\_}1} = \frac{\frac{1}{33}{\sum\limits_{t = 16}^{48}{f_{s}(t)}}}{M}$where f_(s)(t) is a sample of the patient's inspiratory airflow and M isthe mean of inspiratory airflow given by the following:

$M = {\frac{1}{65}{\sum\limits_{t = 1}^{65}{f_{s}(t)}}}$A second shape factor involves a ratio of the Root Mean Square deviationof a midportion of inspiratory airflow and the mean inspiratory airflowaccording to the formula:

${{shapefactor\_}2} = \frac{\sqrt{\frac{1}{33}{\sum\limits_{t = 16}^{48}\left( {{f_{s}(t)} - M} \right)^{2}}}}{M}$Berthon-Jones further discloses a scaling procedure applied to theinspiratory airflow samples such that the mean M of the samples f_(s)(t)is unity (M=1). This scaling procedure simplifies both shape factorformulas. Additional adjustments to f_(s)(t) including averaging and theelimination of samples from erratic breaths such as coughs, sighs,hiccups, etc., are also taught by Berthon-Jones. The foregoing U.S.patent is hereby incorporated by reference.

The present invention involves an improved method and apparatus fordetecting some forms of obstruction based upon the flattening of theinspiratory airflow.

BRIEF SUMMARY OF THE INVENTION

An objective of the present invention is to provide an apparatus inwhich obstruction, either partial or complete, of the patient's airwayis detected by analyzing respiratory airflow.

A further objective is to provide an apparatus in which a novelalgorithm for detecting airway obstruction is implemented without usingadditional components or making substantial changes to the structure ofexisting respiratory apparatus.

Accordingly, a respiratory apparatus is provided in which therespiratory airflow of a patient is continuously monitored. The part ofrespiratory airflow associated with inspiration is identified andsampled. From these inspiration samples, several samples representing amidportion of inspiration are identified. One or more weightingparameters or weighting factors are associated with each midportionsample. These weights and midportion samples are then used to calculatean obstruction index. Finally, this obstruction index is compared to athreshold value which comparison is used to adjust or controlventilatory assistance.

In one embodiment, weighting factors are applied based on whether theinspiratory airflow samples are less than or greater than a thresholdlevel, such as the mean airflow.

In another embodiment, different weighting factors are applied tosamples based on their time positions in a breath. Samples taken priorto a certain event during inspiration, for example, samples precedingthe half way point of inspiration, are assigned lower weighting factorsthan samples succeeding the event. An obstruction index is thencalculated using these samples with their corresponding weightingfactors.

In one aspect, the subject invention pertains to a respiratory apparatuswhich includes a gas source adapted to selectively provide pressurizedbreathable gas to a patient, a flow sensor to sense the respiratoryairflow from the patient and to generate an airflow signal indicative ofairflow, an obstruction detector coupled to said flow sensor whichincludes a weight assigning member arranged to assign several weightfactors to portions of the flow signal and to generate an obstructionsignal using the weighted portions, and a controller coupled to the flowsensor and arranged to control the operation of the gas source, receivethe obstruction signal and alter the operation of the gas source inresponse to the obstruction signal.

Another aspect of the invention concerns an apparatus for monitoringand/or treating a patient having a sleep disorder, the apparatusincluding a flow sensor that senses patient respiration and generates acorresponding flow signal; and an obstruction detector coupled to theflow sensor and adapted to determine a weighted average signal, theweighted average signal being dependent on a weighted average of theflow signal in accordance with one of an amplitude and a time positionof portions of the flow signal, the obstruction detector including asignal generator that generates a signal indicative of an airwayobstruction based on the weighted average signal.

A further aspect of the invention concerns an apparatus for treating apatient having a sleep disorder, the apparatus comprising a mask, a gassource selectively supplying pressurized breathable air to the patientthrough the mask, a flow sensor that senses airflow and generates a flowsignal indicative of respiration, an obstruction detector coupled to theflow sensor and adapted to determine a weighted average signal, theweighted average signal being dependent on a weighted average of theflow signal in accordance with one of an amplitude and a time positionof portions of the flow signal, and a controller receiving theobstruction signal and generating in response a command for activatingthe gas source.

Another aspect of the invention concerns a method for detectingobstruction in the airways of a patient, including measuring an air flowof the patient, detecting a predetermined section of said air flow,assigning weights to portions of said predetermined section anddetermining an index value for said predetermined section based on saidweights as a measure of the obstruction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a respiratory apparatus constructed inaccordance with this invention.

FIG. 2 shows a flow chart illustrating the operation of the apparatus ofFIG. 1.

FIG. 3 shows the inspiration phases of typical respiration signals for ahealthy person and a person with a partial airway obstruction.

FIG. 4 shows a portion of a normal respiration signal from a patient.

FIGS. 5 and 6 show portions of two different respiration signalscharacteristic from patients with sleep apnea.

FIG. 7 shows a flow chart for determining the flattening indices for therespiration signals of FIGS. 4-6.

FIG. 8 shows a normal breathing pattern for a person without respiratoryobstructions to illustrate the determination of two improved obstructionindices.

FIGS. 9, 10, and 11 show various breathing patterns with obstructionsidentifiable using the improved indices.

FIG. 12 shows an example of how a flow curve can be checked to insurethat it is a valid respiration curve.

FIG. 13 shows an example of how a typical respiration flow curve can betrimmed.

DETAILED DESCRIPTION

Apparatus and Methodology

FIG. 1 shows an example respiratory apparatus 10 constructed inaccordance with the invention. The respiratory apparatus 10 includes amask 12 connected to a blower 14 by a flexible tube 16. The mask 12 isfitted to the patient and may be either a nose mask or a face mask. Theblower 14 with an air outlet 22 is driven by a motor 18 in accordancewith control signals from a servocontroller 20. This arrangement allowsthe respiratory apparatus 10 to deliver pressurized air (or air enrichedwith oxygen from a source, not shown). The pressurized air is deliveredby tube 16 to the mask 12. The tube 16 is provided with a narrow exhaustport 26 through which air exhaled by the patient is expelled.

A control circuit 24 is used to control the operation of servocontroller20 and motor 18 using certain predetermined criteria, thereby definingmodes of operation for the apparatus 10. Preferably, in accordance withthis invention, the control circuit 24 is adapted to operate theapparatus 10 to provide CPAP to the patient.

Control circuit 24 includes a flow restrictive element 28. Tubes 30 and31 lead from restrictive element 28 to a differential pressuretransducer 34. Tube 30 is also connected through another tube 33 to amask pressure transducer 32.

The mask pressure transducer 32 generates a first electrical signalwhich is amplified by an amplifier 36 to generate an output P(t)proportional to the air pressure within the mask 12. This output is feddirectly to the servocontroller 20.

The differential pressure transducer 34 senses the differential pressureacross the flow restrictive element 28, which differential pressure isrelated to the air flow rate through the flow restrictive element 28 andtube 16. Differential pressure transducer 34 generates a secondelectrical signal that is amplified by an amplifier 38. This amplifiedsignal F(t) is termed an air flow signal since it represents the airflow through the tube 16.

The air flow signal F(t) is fed to a filter 40 which filters the signalwithin a preset range. The outputs of the filter 40 and amplifier 36 arefed to an ADC (analog-to-digital) converter 42, which generatescorresponding signals f₁ to a microprocessor 44. The microprocessor 44generates analog control signals that are converted into correspondingdigital control signals by DAC 46 and used as a reference signal Pset(t) for the servo 20.

One method for the operation of a respiratory apparatus 10 is shown inthe flow chart of FIG. 2. Individuals skilled in the art will recognizeother methodologies for utilizing the improved flow flattening indexthat is disclosed herein. The embodiment of the methodology of FIG. 2 isalso detailed in U.S. Pat. No. 5,704,345 (the '345 patent). The firststep 100 is the measurement of respiratory flow (rate) over time. Thisinformation is processed in step 102 to generate Index values to be usedas qualitative measures for subsequent processing. Thus, Step 102includes the generation of obstruction index values based upon theweighting method as disclosed herein. Step 104 detects whether an apneais occurring by comparison of the breathing Index with a thresholdvalue.

If the answer in step 104 is “Yes”, an apnea is in progress and therethen follows a determination of patency in step 110. If there is patencyof the airway, a central apnea with an open airway is occurring, and, ifdesired, the event is logged in step 112. If the result of step 110 isthat the airway is not patent, then a total obstructive apnea or acentral apnea with closed airway is occurring, which results in thecommencement or increase in CPAP treatment pressure in step 108. Ifdesired, step 108 may include the optional logging of the detectedabnormality.

If the answer in step 104 is “No”, one or more obstruction indices, suchas the improved flow flattening indices, are compared with thresholdvalues in step 106, by which the determination of obstruction of theairway is obtained. If the answer is “Yes” in step 106, then there is apartial obstruction, and if “No”, there is no obstruction (normalcy).

Step 108 applies in the case of a complete or partial obstruction of theairway a consequential increase in CPAP treatment pressure. In theinstance of normal breathing with no obstruction, the CPAP treatmentpressure is reduced, in accordance with usual methodologies that seek toset the minimal pressure required to obviate, or at least reduce, theoccurrence of apneas. The amount of reduction in step 107 may, ifdesired, be zero. Similarly, in the event of a central apnea with patentairway (step 110,112) treatment pressure is not increased. Suchincreases in pressure reflexively inhibit breathing, further aggravatingthe breathing disorder.

Improved Flow Flattening Indices

FIG. 3 depicts an airflow signal with respect to the inspiratory portionof a typical breathing cycle. During the inspiratory portion of thebreathing cycle of a healthy person, the airflow rises smoothly withinspiration, reaches a peak and falls smoothly to zero. However, apatient with a partially obstructed airway exhibits a breathing patterncharacterized by a significant flat zone during inspiration.Theoretically, for an obstructed flow, as the degree of partialobstruction increases, the airflow signal for inspiration would tend toa square wave.

As previously discussed, the '345 patent describes two shape factorsuseful in testing for a flattening of the inspiratory portion of apatient's breathing cycle. In the preferred embodiment of the invention,the resulting obstruction index or flow flattening index (FFI) for eachshape factor may be compared to unique threshold values. While theapproach works well in many instances, it may not detect certainobstruction patterns.

This can be illustrated by an examination of FIGS. 4-6. FIGS. 4-6 depictportions of respiration cycles. FIG. 4 shows a normal respiration flowand FIG. 5 shows a severely obstructed respiration cycle in which theinspiration period is characterized by two high positive lobes A and Band a relatively flat zone C between lobes A and B. In FIG. 4, the RMSdeviation is indicated by the shaded area under the respiration flowcurve and above the mean inspiration flow. In FIG. 5, the RMS deviationis indicated by the shaded area above the respiration flow curve andbelow the mean inspiration flow. As seen in FIG. 5, due to obstruction,the mean inspiration flow is greater than it would be without the secondpositive lobe B. Therefore, when analyzing the flow using shape factorsof the '345 patent, the highly restricted and abnormal flow of FIG. 5would not be detected as an obstruction.

Similarly, FIG. 6 shows another possible respiration curve for a patientwith a partial airway obstruction. This curve includes an abnormallywide initial positive lobe D preceding a flat portion E. Once again,because of the large lobe D the mean inspiration flow is higher than forthe more typical flow of FIG. 3. Using the prior art obstruction index,this condition may be detected as normal rather than being properlydetected as an obstructed flow.

In order to detect these obstructions while continuing to properlyrespond to non-obstructed flows like the one of FIG. 4, the presentinvention assigns different weighting factors to the inspiration flowsamples depending on:

-   -   (a) the magnitude of each sample with respect to the mean        inspiration flow; and    -   (b) the time-wise position of each sample with respect to a time        reference such as mid-inspiration.

By assigning a different weighting factor to a sample that is less thana particular value, for example, the mean flow, during the obstructionindex or FFI calculation, there is an improved sensitivity to therespiration signal of FIG. 5 without affecting the FFI for normalbreathing where most of the flow is greater than the mean.

Similarly, by assigning a different weighting factor to samples thatoccur after a time reference point, the subsequent samples become moresignificant. This improves sensitivity to the respiration signal of FIG.6 without affecting the FFI for other breaths that are symmetrical intime about the center point of the inspiration.

An algorithm using one form of the invention for calculating theimproved FFI is shown in FIG. 7. In step 100 of FIG. 2, a typical flowrate curve F (defined by a plurality of samples f_(i) where i is anindex from 1 to the total number of samples n) is obtained. In step 200of FIG. 7, the curve F is checked to insure that it is a validinspiration curve. Next, in step 201 the curve F is trimmed to eliminateall samples f_(i) outside of the inspiration period. Methods ofimplementing steps 200 and 201 are discussed in more detail below. Instep 202, a mean M is calculated for all the inspiration samples 1through n using conventional techniques.

In step 204 two weighting factors which may be designated as valuedependent factors w_(i) and time dependent factors v_(i) are assigned toeach of the samples f_(i) based respectively on the amplitude of eachsample and its time position in relation to the inspiration mean M andits center point respectively. For example, the factors w_(i) and v_(i)may be assigned for each flow measurement f_(i) using the followingrules:

A1. If f_(i)>M then w_(i)=1

A2. If f_(i)<M then w_(i)=0.5

B1. If f_(i) is taken prior to the inspiration center point, thenv_(i)=0.75.

B2. If f_(i) is taken after the inspiration center, then v_(i)=1.25.

Next, in step 206 two alternative FFI or obstruction indices arecalculated using the formulas:

$\begin{matrix}{{{value\_ weighted}{\_ index}} = \frac{\sum\limits_{i = j}^{k}{W_{i} \cdot {{f_{i} - M}}}}{M \cdot d}} \\{{{time\_ weighted}{\_ index}} = \frac{\sum\limits_{i = j}^{k}{V_{i} \cdot {{f_{i} - M}}}}{M \cdot d}}\end{matrix}$

Where j is the first and k is the last sample relative to a midportionor center half of the inspiration curve F and d is the number of samplesof the midportion of inspiration or center half as shown in FIGS. 3-6,and M is the mean of the inspiration curve F.

Alternatively, the algorithm may be described by the following steps:

-   -   Check the flow samples to confirm they represent a valid        inspiration cycle with a shape within acceptable bounds.    -   Trim samples from any “pre-inspiratory period”;    -   Find the mean of the inspiration flow samples;    -   Sum the weighed absolute difference of the flow samples from        mean for samples in the center half or mid portion of        inspiration:        -   If flow sample is >mean, sum the difference (flow-mean);        -   If flow sample is <mean, sum ½ the difference;        -   If flow sample is before the center point of the            inspiration, use 75% of the difference from above;        -   If flow sample is after the center point of the inspiration,            use 125% of the difference from above;    -   Scale the sum by the mean and inspiration time to produce the        flattening index: FFI=weighed absolute sum/(Center half        time*mean inspiration flow).

As discussed above, in step 200 of FIG. 7, the curve F is checked toinsure that it corresponds to a valid inspiration curve. The flow curveF is checked against an upper and lower bound to prevent processing ofan inspiratory curve corrupted by a cough, sigh, etc. For example, asshown in FIG. 12, the curve F may be rejected if it exceeds at any timean upper limit curve UL or falls below a lower limit curve LL. UL may beselected at about 150% of the mean inspiratory flow and LL may beselected at about 50% of the mean inspiratory flow.

In step 201 the respiration curve is trimmed to eliminate samples f_(i)occurring before the actual inspiration period. One method of trimmingincludes the steps:

(1) determine the point where the flow reaches 75% of the peakinspiratory flow;

(2) determine the point where the flow reaches 25% of the peakinspiratory flow;

(3) extrapolate a line through these two points to the zero flow line todetermine the point at the beginning of inspiration but use the firstsample if the point is to the left of the first sample.

This trimming method is illustrated in FIG. 13. With reference to thefigure, the respiration curve F crosses the zero flow level at T0. Oncethe maximum inspiratory flow is reached, two intermediate flow levelsare determined: the ¼ inspiratory flow level (i.e. the flow equaling 25%of the maximum inspiratory flow) and the ¾ inspiratory flow level (i.e.the flow equaling 75% of the maximum inspiratory flow). In FIG. 13,curve F crosses these two levels at points F1 and F2, respectively.Using the times T1 and T2, corresponding to the points F1 and F2, thecurve F is approximated by a line L. This line is then extended to thezero flow level to determine an extrapolated time TS as the startingtime for inspiration period for curve F. Samples f₁ obtained prior to TSare ignored.

The improvement resulting from the use of the above described value andtime weighted obstruction indices can be seen with an examination ofsimulated tests. To this end, FIGS. 8, 9, 10 and 11 show breathingpatterns of patients with both normal and obstructed respiration. Thesepatterns were analyzed using the weighted indices of the presentinvention, as well as the shape factor 2 that uses equal weight samplesf_(i) as described in the '345 patent. The results of the tests areshown in the table below.

TABLE I Time weighted Equal weight Index Value weighted index index FIG.8 0.26 0.25 0.25 FIG. 9 0.24 0.139 0.133 FIG. 10 0.31 0.18 0.13 FIG. 110.37 0.27 0.23

The weighted indices range from 0.3, which indicates no flattening orobstruction, to 0, which indicates gross obstruction. The separationpoint between these two classifications is 0.15, which may be used as athreshold value for comparison as described below.

FIG. 8 shows a normal breathing pattern. As can be seen from the table,all three indices have approximately the same value, thereby indicatingthat no increase in CPAP is needed.

FIG. 9 is similar in form to FIG. 5 in that it shows a pattern with twolobes separated by a relatively flat region. As seen in the table, ifthe equal weight index is used, no obstruction is found, while bothimproved indices are below the threshold and, therefore, both indicatean obstructed breathing pattern.

FIG. 10 shows a pattern similar to the one in FIG. 6 that starts offwith a high initial lobe and then decays relatively slowly. For thispattern, the equal weight index and the value weighted index are bothabove the threshold. However, the time weighted index is below thethreshold indicating an obstructed breathing pattern.

Finally, FIG. 11 shows another normal breathing pattern which has ashape somewhat different from the shape shown in FIG. 8. The threeindices in the Table are all above the threshold level therebyindicating a normal pattern as well.

Although the invention has been described with reference to a particularembodiment, it is to be understood that this embodiment is merelyillustrative of the application the principles of the invention. Thus,it is to be understood that numerous modifications may be made in theillustrative embodiment of the invention and other arrangements may bedevised without departing from the spirit and scope of the invention.For example, while the preferred embodiment of the invention appliesweighted samples to formulae which are used to identify a flattening ofairflow, a similar method might be used with other formulae that detectroundness of flow or its deviation there from using a sinusoidal orother similar function.

The invention claimed is:
 1. An apparatus for detecting an upperrespiratory obstruction indicative of sleep apnea comprising: a sensorconfigured to sense a flow of gas breathed by a patient and to generatea flow signal indicative of the gas flow; and an obstruction detectorincluding a processor coupled to said sensor, said obstruction detectorconfigured to evaluate portions of said flow signal and to generate anobstruction signal to indicate an obstruction when the flow signalrepresents an inspiratory pattern having a lobe representative ofrespiratory obstruction.
 2. The apparatus of claim 1 wherein theobstruction detector is further configured to generate an obstructionsignal to indicate an obstruction when the flow signal represents aninspiratory pattern comprising two lobes separated by an approximatelyflat region.
 3. The apparatus of claim 2 further comprising: a gassource configured to selectively provide breathable gas to the patientat a pressure; and a controller including the processor, the controllerconfigured to control a modification of the pressure of the gas sourcein response to the obstruction signal.
 4. The apparatus of claim 3wherein the processor of the obstruction detector is configured toassign different weights to discrete values of the portions based onamplitude of each discrete value.
 5. The apparatus of claim 3 whereinthe processor of the obstruction detector is configured to assigndifferent weights to discrete values of the portions based on timeposition of each discrete value.
 6. The apparatus of claim 3 wherein theprocessor of the obstruction detector is configured to generate theobstruction signal by comparing a threshold to a calculated ratio of amean of a weighted mid-portion of an inspiratory flow signal and a meanof the inspiratory flow signal.
 7. The apparatus of claim 1 wherein theobstruction detector is further configured to generate an obstructionsignal to indicate an obstruction when the flow signal represents aninspiratory pattern comprising an abnormally wide initial lobe followedby a slow decay.
 8. The apparatus of claim 7 further comprising: a gassource configured to selectively provide breathable gas to the patientat a pressure; and a controller including the processor, the controllerconfigured to control a modification of the pressure of the gas sourcein response to the obstruction signal.
 9. The apparatus of claim 8wherein the processor of the obstruction detector is configured toassign different weights to discrete values of the portions based onamplitude of each discrete value.
 10. The apparatus of claim 8 whereinthe processor of the obstruction detector is configured to assigndifferent weights to discrete values of the portions based on timeposition of each discrete value.
 11. The apparatus of claim 8 whereinthe processor of the obstruction detector is configured to generate theobstruction signal by comparing a threshold to a calculated ratio of amean of a weighted mid-portion of an inspiratory flow signal and a meanof the inspiratory air signal.
 12. The apparatus of claim 1 wherein theobstruction detector is configured to generate an obstruction signalupon detection of an inspiratory pattern having two lobes separated byan approximately flat region and to generate an obstruction signal upondetection of an inspiratory pattern having an abnormally wide initiallobe followed by a slow decay.
 13. The apparatus of claim 12 furthercomprising: a gas source configured to selectively provide breathablegas to the patient at a pressure; and a controller including theprocessor, the controller configured to control a modification of thepressure of the gas source in response to the obstruction signals. 14.The apparatus of claim 13 wherein the processor of the obstructiondetector is configured to assign different weights to discrete values ofthe portions based on amplitude of each discrete value.
 15. Theapparatus of claim 13 wherein the processor of the obstruction detectoris configured to assign different weights to discrete values of theportions based on time position of each discrete value.
 16. Theapparatus of claim 13 wherein the processor of the obstruction detectoris configured to generate the obstruction signal by comparing athreshold to a calculated ratio of a mean of a weighted mid-portion ofan inspiratory flow signal and a mean of the inspiratory air signal. 17.The apparatus of claim 1 wherein the generation of the obstructionsignal indicates an obstruction representing an inspiratory patternhaving an initial lobe followed by a flattened section.
 18. Theapparatus of claim 1 wherein the generation of the obstruction signalindicates an obstruction representing an inspiratory pattern having aninitial lobe followed by a decaying section.
 19. A method for detectingan upper respiratory obstruction indicative of sleep apnea comprising:sensing with a sensor a flow of gas breathed by a patient and generatinga flow signal indicative of the gas flow; and detecting an obstructionevent with a processor coupled to said sensor, the processor configuredto control an evaluation of portions of the flow signal and to generatean obstruction signal to indicate an obstruction event when the flowsignal represents an inspiratory pattern having a lobe representative ofrespiratory obstruction.
 20. The method of claim 19 further comprisingthe step of detecting an obstruction event when the flow signalrepresents an inspiratory pattern comprising two lobes separated by anapproximately flat region.
 21. The method of claim 20 further comprisingproviding a breathable gas at a pressure from a flow generator, andcontrolling with the processor a modification of the pressure of thebreathable gas in response to the obstruction signal.
 22. The method ofclaim 21 further comprising assigning, with the processor, differentweights to discrete values of the portions based on amplitude of eachdiscrete value.
 23. The method of claim 21 further comprising assigning,with processor, different weights to discrete values of the portionsbased on time position of each discrete value.
 24. The method of claim21 further comprising comparing, with the processor, a threshold to acalculated ratio of a mean of a weighted mid-portion of an inspiratoryflow signal and a mean of an inspiratory flow signal to generate theobstruction signal.
 25. The method of claim 19 further comprising thestep of detecting an obstruction event when the flow signal representsan inspiratory pattern comprising an abnormally wide initial lobefollowed by a slow decay.
 26. The method of claim 25 further comprising:providing breathable gas to the patient at a pressure with a flowgenerator; and controlling, with the processor, a modification of thepressure of the breathable gas in response to the obstruction signal.27. The method of claim 26 further comprising assigning, with theprocessor, different weights to discrete values of the portions based onamplitude of each discrete value.
 28. The method of claim 26 furthercomprising assigning, with the processor, different weights to discretevalues of the portions based on time position of each discrete value.29. The method of claim 26 further comprising comparing, with theprocessor, a threshold to a calculated ratio of a mean of a weightedmid-portion of an inspiratory flow signal and a mean of an inspiratoryflow signal to generate the obstruction signal.
 30. The method of claim19 wherein an obstruction signal is generated upon detection of aninspiratory pattern having two lobes separated by an approximately flatregion and an obstruction signal is generated upon detection of aninspiratory pattern having an abnormally wide initial lobe followed by aslow decay.
 31. The method of claim 30 further comprising delivering aflow of breathable gas at a pressure by a flow generator; andcontrolling, with the processor, a modification of the pressure of thebreathable gas in response to the obstruction signals.
 32. The method ofclaim 31 further comprising, assigning, with the processor, differentweights to discrete values of the portions based on amplitude of eachdiscrete value.
 33. The method of claim 31 further comprising,assigning, with the processor, different weights to discrete values ofthe portions based on time position of each discrete value.
 34. Themethod of claim 31 further comprising comparing, with the processor, athreshold to a calculated ratio of a mean of a weighted mid-portion ofan inspiratory flow signal and a mean of the inspiratory flow signal togenerate the obstruction signal.
 35. The method of claim 19 wherein thegeneration of the obstruction signal indicates an obstructionrepresenting an inspiratory pattern having an initial lobe followed by aflattened section.
 36. The method of claim 19 wherein the generation ofthe obstruction signal indicates an obstruction representing aninspiratory pattern having an initial lobe followed by a decayingsection.
 37. An apparatus for monitoring or treating a patient havingsleep disorder, said apparatus comprising: a flow sensor to generate aflow signal indicative of the patient's respiration; and an obstructiondetector coupled to said flow sensor arranged to generate an obstructionsignal when said flow signal has, during an inspiratory portion of abreathing cycle, two high positive lobes and a relatively flat zonebetween the lobes.
 38. A method for determining the presence of anobstruction of the airway of a patient, the method comprising: accessingdata samples of a signal generated by a flow sensor, the data samplesrepresenting airflow of a patient's airway; and generating anobstruction signal in an obstruction detector coupled to said flowsensor when at least one breathing cycle in the sampled flow signal has,during an inspiratory portion, two high positive lobes and a relativelyflat zone between the lobes.
 39. An apparatus for monitoring or treatinga patient having sleep disorder, said apparatus comprising: a flowsensor to generate a flow signal indicative of the patient'srespiration; and an obstruction detector coupled to said flow sensorarranged to generate an obstruction signal when said flow signal has,during an inspiratory portion of a breathing cycle, an abnormally wideinitial positive lobe preceding a relatively flat portion.
 40. A methodfor determining the presence of an obstruction of the airway of apatient, the method comprising: accessing data samples of a signalgenerated by a flow sensor, the signal representing airflow of apatient's airway; generating an obstruction signal in an obstructiondetector coupled to said flow sensor when at least one breathing cyclein the sampled flow signal has, during an inspiratory portion, anabnormally wide initial positive lobe preceding a relatively flatportion.